linux-kernel - Re: [PATCH 1/1] [virt] virtio-blk: Use ida to allocate disk index

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Date:	Thu, 09 Jun 2011 08:51:05 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mark Wu <dwu@...hat.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	tj@...nel.org, Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH 1/1] [virt] virtio-blk: Use ida to allocate disk index

On Wed, 08 Jun 2011 09:08:29 -0400, Mark Wu <dwu@...hat.com> wrote:
> Hi Rusty,
> Yes, I can't figure out an instance of disk probing in parallel either, but as
> per the following commit, I think we still need use lock for safety. What's your opinion?
> 
> commit 4034cc68157bfa0b6622efe368488d3d3e20f4e6
> Author: Tejun Heo <tj@...nel.org>
> Date:   Sat Feb 21 11:04:45 2009 +0900
> 
>     [SCSI] sd: revive sd_index_lock
> 
>     Commit f27bac2761cab5a2e212dea602d22457a9aa6943 which converted sd to
>     use ida instead of idr incorrectly removed sd_index_lock around id
>     allocation and free.  idr/ida do have internal locks but they protect
>     their free object lists not the allocation itself.  The caller is
>     responsible for that.  This missing synchronization led to the same id
>     being assigned to multiple devices leading to oops.

I'm confused.  Tejun, Greg, anyone can probes happen in parallel?

If so, I'll have to review all my drivers.

Thanks,
Rusty.

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